The present invention relates to a tremolo unit mechanism for an electric guitar, capable of rapidly and periodically varying a tension of strings to vary the pitch, thereby obtaining a special acoustic effect, a so-called tremolo effect.
A Fender type tremolo mechanism is known as a conventional tremolo unit, mechanism for an electric guitar. According to the Fender type tremolo mechanism, a bridge base vertically pivotally disposed on a body of an electric guitar is balanced with a moment due to a tension of strings by means of balancing springs, this balanced state is destroyed by a vertical movement of a tremolo arm, and the bridge base is pivoted to repeatedly vary the tension of the strings, thereby obtaining the tremolo effect.
In such a conventional tremolo unit mechanism, the pitch can be varied by pivoting the bridge base vertically from its rest position. However, a balanced state between the moment of the tension of the strings and that of the balancing springs tends to be destroyed when a tremolo arm is not operated, thereby posing a problem in terms of pitch stability during a non-tremolo performance.
In addition, when the string is strongly touched, the tremolo unit mechanism vibrates slightly, so that a musical tone fluctuation (pitch instability) undesirably remains.
In order to eliminate the above problems, the present inventor has recently proposed a tremolo unit mechanism in which a stopper screw is disposed in the bridge base to abut against the body at its lower end, thereby controlling pivotal movement of the bridge base toward the body to stabilize the bridge base. However, in this mechanism, since the stopper screw is disposed in the bridge base, size and weight of the bridge base are increased to increase moments of inertia thereof, so that a lingering tone undesirably remains when a tremolo arm is operated. Furthermore, in order to adjust a height of the bridge base over a wide range, the stopper screw needs to be vertically moved by about at least 10 mm, resulting in an upper end portion of the screw inconveniently projects upward from the bridge base.
In addition, in the tremolo unit mechanism of this type, the above-mentioned balanced state is easily destroyed to vary the pitch when a hand and the like touches the tremolo arm during a performance, so that the tremolo unit mechanism must be locked during a non-tremolo performance. For this reason, various lock mechanisms have been conventionally proposed to lock the tremolo unit mechanism. Examples are an "arm lock" device available from Fernandez Corp. and a lock mechanism of a tremolo unit mechanism disclosed in Japanese Utility Model Laid-Open No. 56-75793.
However, according to the former arm lock device, the bridge base can be locked only at a position where a cam engages with a groove and hence cannot be locked at given positions. On the other hand, according to the latter lock mechanism, the bridge base can be advantageously locked at a given position. However, when the bridge base is unlocked, a rotation cam abuts against lock pins against a performer's wish, resulting in a poor movement of a bridge assembly and hence in unstable tuning. In order to prevent this, accuracy of components and assembly must be improved, thereby causing high cost.